1. Field of the Invention
This invention relates generally to the field of thermal monitoring and more particularly to the field of measuring temperatures during semiconductor operations.
2. Description of the Related Art
As semiconductor integration continues to make advances, the packaging densities of semiconductor devices continues to increase. The number of transistors on semiconductor devices has doubled every couple of years. This continued integration of more electronic circuitry into semiconductor devices is not without undesirable consequences.
One of these undesirable consequences or side-effects is the increase in heat generated due to the increase in packaging density. Several solutions have been employed for removing heat from semiconductor devices. These solutions include heat sinks, cooling fans, and in some cases, liquid cooling. Today many commercially available semiconductor devices, especially microprocessors, such as those used in personal computers from Intel, AMD, IBM, Cyrix and others, ship with attached cooling fans. Typically these cooling fans are fastened as part of a heat sink onto the top side of the semiconductor device. Although these work well in many applications, the operating temperature of the semiconductor device is not monitored and therefore not known during the operation of the semiconductor device.
To overcome this problem, providers of semiconductor devices have been integrating temperature sensors directly into the cavity of the socket for plugging in the semiconductor device. A socket refers to a receptacle, usually soldered to a printed circuit board, for plugging in the semiconductor device. The use of temperature sensors, such as thermal-couples and thermistors, enables the monitoring of a semiconductor device during operation and notifies the operator if the temperature is out of a desired operating range. This is particularly important in applications where predicting that a semiconductor device may start operating out of range is important. For instance, the use of a semiconductor device in a machine for an industrial manufacturing application or for use in a mission critical application such as a PC server for a business.
The use of a temperature sensor, although it enables monitoring, out-of-temperature alarming and semiconductor device failure prediction, is not without its shortcomings. One shortcoming when using a temperature sensor embedded in the cavity of a socket for plugging a semiconductor device is accounting for the difference in the temperature between the semiconductor device and the temperature measured by the sensor itself. Several semiconductor manufacturers rate the temperature operating range of semiconductor devices as the temperature measure at the top center of the semiconductor device. Measuring the operating temperature of a semiconductor device is difficult in applications where the top of the device is covered by a heat sink, a fan, or both. Therefore a need exists to relate the temperature directly provided by manufacturers for the top of a semiconductor device with the temperature specified by a sensor embedded in the cavity of the socket underneath the semiconductor device.
Still, another shortcoming of using a temperature sensor embedded in a socket is the need to adapt the monitoring of temperature ranges for pin compatible semiconductor devices. Pin compatible semiconductors have different operating temperature ranges. It is not uncommon for one manufacturer of a pin compatible semiconductor to have a temperature range that is different from another manufacturer of the same pin compatible device. In addition, pin compatible semiconductor devices, such as microprocessors, are available in several clock speeds. One example is an Intel Pentium II running at 233 MHZ and a Pentium II Chip running at 400 MHZ. The temperatures for these pin compatible semiconductor devices may be different. Accordingly a need exists to provide a method and apparatus to monitor the operating temperature of a pin compatible semiconductor devices that can accommodate different temperature characteristics.
Yet, another shortcoming for the manufacturers of a pin compatible semiconductor devices, is the presumption of consistencies in the packaging of semiconductors. For example, the bottom surface the semiconductor device may have indentations, and other irregularities that do not provide a direct contact to the sensor. Heat from the device is transferred by conduction through the trapped air spaces between the top of the device socket and the bottom of a semiconductor device. Experiments have shown that a major source of heat transfer from a semiconductor device is through the metallic pins mounted to the semiconductor device. Heat is conducted through the metallic pins of the semiconductor device, through the metallic receptacles of the socket and through to the circuit board. This heat transfer path circumvents heat transfer directly to the sensor. Instead, heat is transferred from the device back up through the socket through the circuit board to the sensor. Accordingly, a need exists to provide a method and apparatus to measure the temperature of semiconductor devices to overcome these problems